The present invention relates to tire pressure monitoring systems and, more particularly, to the characterization of a low-pressure or high-pressure condition occurring in one or more tires of a set of tires mounted on the vehicle, and most particularly, to identification of the location or particular wheels of the vehicle that the particular tire or tires are located.
There are several advantages to maintaining the pneumatic tires of an automobile at the inflation pressure recommended by the tire or vehicle manufacturer. Vehicle handling characteristics are maintained when all tires are inflated to the condition specified by the vehicle designer. The loss of pressure in one or more tires on the vehicle may result in less than optimum driver control and therefore a reduced safety condition. Inadvertent over-inflation of one or more tires may also result in less than optimum vehicle handling. Operating a vehicle with tire pressures outside the recommended inflation range can also reduce tire life due to excessive flexing and heating and resultant fatigue or wear. Also, operating a vehicle with under-inflated tires can significantly decrease fuel efficiency. Tire pressure monitoring systems have been developed which alert the vehicle operator when the pressure in one or more of the tires fitted to the vehicle is outside a predetermined range.
So called run-flat tires can puncture and lose air pressure without the drivers knowledge. The tire manufacturer typically specifies a distance and maximum speed for operation in the run-flat condition. It is important for the driver to know when the run flat condition occurred so that operating the tire beyond its safe limits may be avoided. Consequently, tire pressure monitoring systems are typically installed on vehicles equipped with run-flat tires, but due to the dangers associated with sudden tire degradation on the likes of sports utility vehicles and the like, tire monitoring systems are being used widely on many types of vehicles.
Indeed, following an increase in public awareness of the potential consequences of operating tires outside the manufacturers recommended pressure range, legislation has been introduced such as proposed FMVSS 138 which requires that a tire pressure monitoring system be installed as original equipment on all new vehicles sold in the United States after November, 2003.
While several tire pressure-monitoring methods have been proposed, two general approaches have been favored. One is indirect and relies on the determination of the rolling radius of each hub and tire assembly (and often linked to the anti-lock brake system (ABS) of the vehicle). The second is direct and relies on the wireless transmission of a signal from a transducer module installed in the pressurized cavity of each tire. Such systems work well for their intended purposes, but there are disadvantages.
The rolling radius method relies on the signals generated by wheel rotation sensors, typically installed as part of an anti-lock braking system. The rolling radius represents the actual radius from the center of the tire to the generally flattened area of the tire in contact with the ground. Because of the flattening at the point of contact of the tire and the road or surface, the rolling radius measures smaller than the nominal radius of the tire as manufactured or unloaded, since the nominal radius does not account for variation in pressure within the tire and load on the tire. Since the rotational speed of each wheel is known accurately, the rolling radius of the hub and tire assembly mounted at each wheel can be inferred. This system of tire pressure monitoring (frequently referred to in the art as ABS-tire pressure monitoring) does not, however, provide absolute values of pressure, nor does it provide tire temperature information. If all of the tires on the vehicle were to lose pressure equally over time, such a system may fail to detect a reduction in pressure in any tire. Also, this system requires that data be gathered over some minimum number of wheel rotations in order to allow tire temperatures to equalize to some extent, to determine relative rolling radii, and then to approximate each tire pressure. This type of system is not well suited to anything other than installation as original equipment. While this type of system is a low cost addition to a vehicle equipped with anti-lock brakes, it has many performance shortcomings. Since the wheel rotation can only be monitored when the wheel is rotating, this type of system cannot be used to monitor the condition of a spare tire carried on the vehicle, nor can it provide an instant indication of a flat tire when the ignition switch is operated. It is not uncommon to have a slow air leak from a tire due to the penetration of a sharp object such as a nail, screw or other small metallic object, through the tire wall, typically in the tread area. Such a rate of pressure loss may not cause the driver to notice the condition while driving, but when left for a prolonged period, such as overnight parking, the pressure loss may result in a sufficiently flat tire such that driving the vehicle may permanently damage or weaken the tire. Since the driver may approach the vehicle without sight of the damaged or at least partially deflated tire, it is preferable that the pressure monitoring system provides warning immediately on operation of the ignition switch.
The direct sensing method requires the installation of a wireless module in contact with the gas within the pressurized cavity of each tire and hub assembly. A matched receiving module is installed on a fixed portion of the vehicle such that the transmitted data may be processed and presented to the vehicle operator as required. A receiver may be positioned within each wheel well of the vehicle, in which case it is necessary to install one receiver for each monitored tire on the vehicle, or, a single receiver may be placed approximately centrally within the vehicle, such as at the interior rearview mirror location. The advantages of multiple receivers are that transmission distances can be short, thus conserving power, and that data is associated with the receiver location, thus avoiding system training. The significant disadvantage of multiple receivers is the high additional cost. Additionally, installation is difficult unless as original equipment. The potential disadvantages of a single receiver include more complex coding to avoid transmitter confusion, and the need for a greater transmission range, both of which have adverse power implications. A significant disadvantage of the single receiver approach is the need for system training. Each transmitter in the system is identified by a unique code so the receiver always associates data with a particular tire being monitored by a particular pressure sensor but, without a complex and currently impractical antenna configuration, the system cannot determine the wheel location that the particular tire is actually located on. Also, since tires are commonly rotated or replaced by a spare, it is necessary to train the system. Training may consist of manually reducing the air pressure in a predetermined tire until the system indicates it has detected a loss of pressure, re-inflating to the correct pressure and, repeating for all other monitored tires in the system in a predetermined sequence. Training must be repeated whenever a receiver position is changed.
It is known to identify the tire location by utilizing a temperature sensor and an accelerometer sensor at each tire of the vehicle, such as disclosed in U.S. Pat. No. 6,259,361, which is hereby incorporated herein by reference. The temperature sensor may indicate whether it is positioned at the front or rear tires due to temperature differences typically present between the front and rear tires. The accelerometer sensor may determine a rolling direction of the tires, in order to determine whether the tires are on the left or right side of the vehicle. Such a pressure sensing system may include multiple components and/or systems, in addition to the pressure sensors at each tire, and thus may be complex and expensive to implement.
Thus, there is a need for an improved tire pressure monitoring system that overcomes the above disadvantages.
The present invention is intended to provide a self training tire pressure monitoring system which may sense the tire pressure of each tire of a vehicle with a respective pressure sensor and may determine at which wheel of the vehicle wheel set that the particular tire being monitored with the pressure sensor is located. The tire pressure and the respective location or wheel of the tire may be displayed at a display of the vehicle.
According to an aspect of the present invention, a self training tire pressure monitoring system for a vehicle having a set of tires includes first and second pressure sensors, first and second wheel sensors and a control. The pressure sensors are positioned at respective tires of a set of tires of the vehicle. The pressure sensors are operable to provide measured pressure outputs indicative of the actual measured gaseous pressure (i.e., typically air pressure) of the respective tires that inflates the respective tires. The wheel sensors are positioned at the wheels of the vehicle. The tires are mounted on respective wheels. The wheel sensors are operable to provide characteristic outputs indicative of rotation of the respective wheels. The control receives the characteristic outputs and the measured pressure outputs and is operable to deduce a deduced characteristic indicative of pressure variation in the tire mounted on a particular wheel in response to the characteristic output indicative of rotation of the particular wheel. The control is operable to integrate, such as by comparison or by other algorithmic and/or computational manipulation, the actual measured pressure outputs and the deduced characteristic signatures to associate the pressure sensors and respective tires with the particular location or wheels at which the particular pressure sensors and tires are positioned. A display is operable to indicate the measured pressure of the tire at a particular wheel of the vehicle.
Preferably, the control is operable to correlate the pressure outputs (as received, preferably in real time, from the pressure sensors at the tires) with the deduced characteristics (preferably calculated from data received from a rolling radius monitoring or deducing system) to match the pressure output of each of the pressure sensors with one of the deduced characteristics. Preferably, the control is operable to deduce the deduced characteristics over a period of time to define deduced characteristic signatures indicative of pressure variations in the tires mounted on the particular wheels over the period of time. Preferably, the control is operable to deduce the deduced characteristic in response to at least one a rolling radius of the tires, a temperature of the tires, a wheel speed of the tires, a wheel rotation of the tires, a wheel position of the tires, a vehicle speed, a differential of the vehicle and a wheel slip sensor of the vehicle.
In one form, the control is operable to deduce a deduced rolling radius for the tire mounted on each wheel in response to the characteristic outputs. The deduced rolling radius may be calculated in response to a rotation of the wheels and a vehicle velocity. The deduced rolling radius may be calculated over a period of time to define deduced rolling radius signatures. The control is operable to correlate the measured pressure outputs with the deduced rolling radius signatures to match the pressure outputs of the pressure sensors with the deduced rolling radius signatures.
In another form, the pressure sensors are operable to provide the actual measured pressure output to the control via a radio frequency communication link. The pressure sensors may include a pressure transducer, a temperature sensing means, a processor and a transmitter. The control may include an antenna and a receiver.
According to another aspect of the present invention, a method for determining a pressure and location or wheel of at least two tires of a vehicle includes sensing a measured pressure within at least two tires of a vehicle in response to pressure sensors at respective tires of the at least two tires and deducing a deduced characteristic signature at respective wheels which is indicative of pressure variations in the tires mounted at the respective wheels of the vehicle. The measured pressures and the deduced characteristic signatures are correlated to determine the location or particular wheel at which each of the tires is mounted. The measured pressure of the tire and the particular wheel of the vehicle at which the tire is mounted is displayed on a display of the vehicle.
Preferably, the method includes communicating the sensed pressure to a control via a radio frequency communication link. Preferably, the deduced characteristic signature is deduced over a period of time to define a time dependent deduced characteristic signature.
Preferably, the deduced characteristic signature is deduced in response to a deduced rolling radius of the at least two tires of the vehicle, a temperature of the at least two tires, a wheel speed of the at least two wheels, a wheel position of the at least two wheels, a wheel rotation of the at least two wheels, a speed of the vehicle, a differential of the vehicle and/or a wheel slip sensor of the vehicle. Preferably, the deduced characteristic signatures are deduced in response to an estimated rolling radius of each of the at least two tires. The rolling radius may be determined or approximated in response to an input from a wheel speed sensor, a wheel rotation sensor, a wheel position sensor, a rotary encoder, a vehicle speed sensor, a temperature sensor, a steering wheel, a differential, a wheel slip sensor and/or the like.
According to yet another aspect of the present invention, a self training tire pressure monitoring system for a vehicle having a set of tires includes at least two pressure sensors, at least two wheel sensors, a control and a display. The at least two pressure sensors are positioned at respective tires of a set of tires of the vehicle. The at least two pressure sensors are operable to provide a measured pressure output indicative of the actual pressure of the respective tires. The wheel sensors are positioned at respective wheels of the vehicle. The wheel sensors are operable to provide a wheel rotation output indicative of rotation of the respective wheels. The control receives the measured pressure outputs and the wheel rotation outputs and deduces a deduced rolling radius for the tire mounted at a particular wheel in response to the wheel rotation output indicative of rotation of the particular wheel. The control is operable to integrate the measured pressure outputs and the deduced rolling radii to determine the particular wheels at which the pressure sensors and associated tires are positioned. The display is operable to indicate the measured pressure of the tire and the particular wheel at which the tire is mounted.
Therefore, the present invention provides a self training tire pressure monitoring system which is operable to determine the tire pressure of at least two tires of a vehicle and to determine at which of the wheels of the vehicle the detected pressures and associated tires are positioned. The tire pressure monitoring system of the present invention may include a wireless communication with the tire pressure sensor at each tire of the vehicle and may determine where the sensor and tire have been moved to, such as when the tires are rotated on the vehicle to minimize uneven wear of the tires. The tire pressure monitoring system of the present invention provides for generally continuous monitoring of tire pressure irrespective of vehicle movement and may provide an indication of a flat tire before the vehicle is moved. The tire pressure monitoring system may detect a change in pressure of a tire of the vehicle and may indicate which tire is experiencing the change in pressure and at which wheel the tire is located. The tire pressure monitoring system may indicate the pressure for each tire and may indicate the location of the tires on the vehicle with a single receiver and control positioned within the interior of the vehicle, thereby reducing the costs of the monitoring system. The tire pressure monitoring system of the present invention automatically determines the location or wheels at which the particular pressure sensors and tires are located, without requiring manual training of the control each time the tires are changed or rotated. The location of the pressure sensors and tires may be determined by comparing the measured pressures in the tires with a deduced characteristic or deduced characteristic signature, such as a characteristic signature indicative of variations or undulations in the rolling radius of the tires and/or the pressure in the tires.
These and other objects, advantages, purposes, and features of the present invention will become more apparent from the study of the following description taken in conjunction with the drawings.